Test if a changeset has recorded any changes.

Return non-zero if no changes to attached tables have been recorded by
the session object passed as the first argument. Otherwise, if one or
more changes have been recorded, return zero.

Even if this function returns zero, it is possible that calling
sqlite3session_changeset() on the session handle may still return a
changeset that contains no changes. This can happen when a row in
an attached table is modified and then later on the original values
are restored. However, if this function returns non-zero, then it is
guaranteed that a call to sqlite3session_changeset() will return a
changeset containing zero changes.